Cellulosic materials coated with an organic polycarbodiimide



United States Patent 3,450,562 CELLULOSIC MATERIALS COATED WITH ANORGANIC POLYCARBODIIMIDE Guenther Kurt Hoeschele, Wilmington, Del.,assignor to E. I. du Pont de Nemours and Company, Wilmington, Del., acorporation of Delaware No Drawing. Filed June 18, 1965, Ser. No.465,145 lint. Cl. C08c 17/16; C0811 13/16; (309d 3/48 U.S. Ql. 117-155 8Claims ABSTRACT OF THE DISCLOSURE Cellulosic materials coated on atleast one surface with an organic polycarbodiimide having at least twocarbodiimide groupings, said polycarbodiimide being dispersed ordissolved in a liquid carrier; the coating of at least one surface ofsaid material is followed by drying and/or heating to improve thecompressive strength of the coated material under high moistureconditions.

Products made from cellulosic materials are commonplace items in ourpresent civilization. Paper and cardboard are particularly familiarexamples. Cellulosic products are of great economic importance and areused in a wide variety of valuable applications, packaging being one ofmany. For some purposes it would be desirable to improve the propertiesof these materials. For instance, improved compression strength underhigh-moisture conditions is especially needed by corrugated papercontainers. Although this type of packaging material has generally givensatisfactory service under dry or low-moisture conditions, it has thedisadvantage of losing a large portion of its strength when exposed to avery humid or high moisture environment. Boxes are often stacked inwarehouses where the humidity becomes quite high. Frequently, the fullcapacity of the storage area is not utilized because boxes withinsufficient top-to-bottom compressive strength topple. Fruit andvegetable growers need a more rigid package to minimize moistureproblems that result when the containers they use are moved in and outof refrigerated areas to transport the products to the consumer.Military shipments are frequently sent to tropical areas where thehumidity is high for prolonged periods of time.

It is a common practice today to resort to the use of heavier weightpaper board components when the box fabricator is confronted with theproblem of supplying a more rigid corrugated container for a highhumidity application. While this heavier board gives some extrarigidity, it also adds to the weight of the container and increases thecost of shipment accordingly.

Coatings, such as waxes and films, have been applied to boxes forshipment and storage of produce which may be subjected to ice or water.Although such coatings are often elfective in excluding liquid water,they are frequently ineffective when boxes are exposed to high humidityfor lengthy periods.

Accordingly, it is an object of the present invention to providecellulosic materials which display improved properties such ascompressive strength under high moisture conditions.

The above and other objects which will become apparent hereinafter areachieved by providing a cellulosic web having at least one surfacecoated with an organic polycarbodiimide.

Preferably the polycarbodiimide should be present in an amount of fromabout 1 to about 15% by weight of the cellulosic web, higherconcentrations, up to about 30% are useful, although this is notcritical.

The polycarbodiimide is applied to a preformed cellulosic web using aliquid carrier which can be water or an organic liquid or mixturesthereof. The polycarbodiimide is used as a solution, an emulsion, or adispersion. In one embodiment, the polycarbodiimide is applied to thecellulosic web in the form of a solution in an organic liquid containingat least 10% by weight of a super solvent and in the absence of water.In another embodiment the polycarbodiimide is dissolved in a suitablesolvent, the solution emulsified with water and the emulsion applied tothe cellulosic web. The polycarbodiimide can also be applied in the formof a dispersion of solid particles in water or other liquid.

The concentration of the polycarbodiimide in the liquid carrier is notcritical. The concentrations which can usefully be employed depends onthe polycarbodiimide selected, upon its molecular weight and upon theparticular method chosen for applying the polycarbodiimide to thecellulosic web. In general, however, concentrations of about 2 to about50% by Weight of the polycarbodiimide in the liquid carrier are suitablefor the practice of this invention. In some modern high speed coatingtechniques, even higher concentrations up to 90% can be used.

carbodiimide polymers which are useful in the present invention may bemade by polymerizing organic polyisocyanates. Representative examples ofthe latter include: toluene 2,4 diisocyanate; an isomer mixturecontaining 2,4- and 20% 2,6-toluene diisocyanate;4,4'-methylenebis-(phenyl isocyanate);4,4-methylenebis(o-tolylisocyanate); 5-chloro-toluene-2,4-diisocyanate;m-phenylene diisocyanate, owl-toluene diisocyanate, 1,6-hexamethylenediisocyanate, methylene bis(4-cyclohexyl-isocyanate) andbis(2-isocyanato ethyl) carbonate. The invention is applicable to notonly the pure distilled polyisocyanates but the undistilled reactionproducts resulting from the phosgenation of an organic polyamine.Procedures for making the polycarbodiimide polymers and representativeexamples are given in US. Patents 2,941,966; 2,941,983; 3,152,- 131; and3,157,662.

The preferred materials are urethane-terminated aromaticpolycarbodiimides which are described in US. Patent 2,941,983 andcarbodiimide-terminated aromatic polycarbodiimides obtained frommixtures of monoand polyisocyanates.

The term aromatic in this connection is used to signify that thepolycarbodiimide contains aromatic groupings which can be benzene ornaphthalene rings, the carbodiimide groups being directly attached to anaromatic nucleus. The aromatic nucleus can be substituted withsubstituents which are inert to the carbodiimide linkages, includingalkyl, cycloalkyl, aryl, aralkyl, alkoxy, aryloxy, unsaturated groupssuch as vinyl, allyl, butenyl groups, halogen particularly fluorine orchlorine, nitrile, nitro groups and the like.

While the aromatic polycarbodiimides are preferred, aliphaticcycloaliphatic and aliphatic-aromatic polycarbodiimides or mixturesthereof can be used in the process of this invention.

Urethane-terminated aromatic polycar-bodiimides are made by adding acatalyst for carbodiimide formation to an aromatic polyisocyanate or anisocyanate terminated polymer or their mixtures, initiating chainextension, and finally stopping the polymerization by adding a primaryor secondary alcohol when the polymer has reached a certain desirednumber-average molecular weight. Preferably the alcohol is a long chainaliphatic alcohol having from 8 to 20 carbon atoms, including loweralkyl monoethers of polyethylene and polypropylene glycols such as themonoethyl ether of diethylene glycol or the monomethyl ether oftripropylene glycol. The use of a longchain alcohol to form aurethane-terminated polycarbodiimide tends to lower the melting point ofthe polycarbodiimide, in some cases forming a conveniently handledliquid product. In addition to alcohols other capping agents which donot readily undergo reaction with the carbodiimide function may also beemployed. Aromatic primary amines such as aniline and toluidine,aromatic hydroxy compounds such as phenol and the cresols lactams suchas epsilon caprolactam, ketoximes, or other compounds containing activehydrogen may be employed for this purpose. Chain termination by additionof monoisocyanates is of particular interest for preparingpolycarbodiimide compositions having a high carbodiimide content.Because these polycarbodiimides can not form intramolecular hydrogenbonds, the lower molecular weight products are relatively low viscosityliquids. By varying the ratio of monoisocyanate to polyisocyanate themolecular weight of the resulting polycarbodiimide can be controlledover a wide range. Less reactive monoisocyanates can be mixed with thepolyisocyanate at the beginning of the polycarbodiimide reaction oradded to the isocyanateterminated polycarbodiimide during the reaction.More reactive monoisocyanates are preferably added slowly topolycarbodiimide reaction mixture to avoid extensive monocarbodiimideformation by self-condensation of the monoisocyanates. Theseconsiderations are discussed in J. Org. Chem. 28, 2072 (1963).Representative monoisocyanates are phenylisocyanate, o-tolylisocyanate,4-chlorophenylisocyanate and cyclohexylisocyanate. The end cappedproducts show satisfactory stability in solution and, hence, areparticularly suited for the purposes of this invention.

As indicated hereinabove, polycarbodiimides which have not beenend-capped i.e. which contain isocyanato end groups, can also be used.However inasmuch as these materials are not too stable in solution, itis generally necessary to prepare the solution of the polycarbodiimideimmediately before the coating operation. The polymerization reactioncan also be carried out concurrently with the coating operation i.e. anaromatic polyisocyanate is mixed with a catalyst for its polymerizationapplied to the cellulosic web, and then permitted to polymerize incontact therewith.

The polycarbodiimides must contain at least two carbodiimide groupings.Carbodiimides containing only one carbodiimide grouping are noteffective in the practice of the present invention. Since thepolycarbodiimides are formed in a polymerization reaction, mixedproducts are obtained containing 1, 2, 3 or more carbodiimide groupings.These materials are relatively difiicult to separate and are normallyemployed as a mixture. In this case the functionality or number ofcarbodiimide groups per molecule is specified as an average, thus thefunctionality of a compound having two carbodiimide groups is 2; anequimolar mixture of a polycarbodiimide having two carbodiimide groupswith a polycarbodiimide having three carbodiimide groups would have afunctionality of 2.5; polymers having an average functionality of atleast two are suitable for the practice of this invention. The upperlimit of molecular weight or average molecular weight is not critical.Generally, the polycarbodiimides should contain from 2 to 30 weightpercent of N=C= groups. The higher molecular weight polycarbodiimideshaving melting points above about 150 C. tend to be insoluble in organicsolvents and are therefore diflicult to apply by solution techniques.Accordingly, it is preferred to employ polycarbodiimides having meltingpoints less than 150 C.

In preparing the treated cellulosic webs of the present invention, it isnecessary to disperse or dissolve the polycarbodiimides in a liquidcarrier and apply the resulting mixtures to at least one surface of thecellulosic substrate. When the polycarbodiimide is applied fromsolution, the liquid carrier can be any of the solvents which have beenused for the preparation of the polycarbodiimide itself, for example, asdescribed in US. Patents 2,941,983, and 2,941,966. Examples includeethyl acetate, toluene, methylene chloride, dimethyl sulfoxide,tetrahydrofuran and acetone. The best properties are obtained when thepolycarbodiimide is applied from solution in a super solvent.

Super solvents are a special class of solvents which are known in theart and which have found use in dissolving linear polymers such aspolyamides, polyesters, polyacrylonitrile and various linearpolyurethanes, and linear polyureas. The super solvents are essentiallyneutral and many are completely miscible with water, but this is not arequirement. Super solvents may be solids at room temperature which formliquid solutions with the polycarbodiimide. The super solvents are inerttoward carbodiimide groups in that they are free of reactive groups suchas hydroxy or amino groups. In particular, the types of super solventswhich are preferred for making the carbodiimide solutions include:N-alkylated ali hatic amides; N-alkylated ureas; N-alkylatedsulfonamides; sulfoxides; and sulfones.

The N-alkylated aliphatic amides, may be represented by the generalformula:

wherein R R and R may be alkyl, cycloalkyl, or arylalkyl, whereby thefully alkylated or N,N-dialkyl aliphatic amides are obtained. R may alsobe hydrogen. R R and R may be independently selected as long as thetotal number of carbon atoms contained in the three groups does notexceed 24. R R and R may bear substituents which are inert towardcarbodiimide groups such as halogen and alkoxy. R or R; can be hydrogenwhereby the corresponding N-alkyl aliphatic amides will be obtained. Rand R can be alkylene groups and form a ring which may or may notcontain a hetero-atom such as sulfur or oxygen. This general formula mayalso be used to represent an alkylated cyclic amide which would beformed by R with either R or R whereby the amide linkage is part of thecyclic structure. Diamides derived from dicarboxylic acids arecontemplated for use since they contain the required alkylated amidestructure. Suitable compounds represented by this general formulainclude N- methyl formamide, N-methyl acetamide, N-butylstearamide,N,N-dimethyl-formamide, N,N-dimethylacetamide, N,N-di-n-butylformamide,N,N-dimethylcaprylamide, N, N-dimethylstearamide, N-formylpiperidine,N-acetylpyrrolidine, N-formylmorpholine, N,N,N',N-tetramethyl oxalamide,N,N,N,N'-tetramethyladipamide, pyrrolidone, epsilon-caprolactam,N-methylpyrrolidone and N,N-di-nbutylacetamide. Especially preferred areN,N-dimethylformamide, N-N-dimethylacetamide and N-methylpyrro lidone.The fully alkylated ureas are closely related to amides and in a sensemay be considered as diamides of carbonic acid. The alkylated ureas maybe represented by the general formula:

wherein R R R and R may be alkyl, cycloalkyl or arylalkyl. The groupsmay be selected independently as long as the total number of carbonatoms in the four groups does not exceed 24. A preferred urea isN,N,N,N'- tetramethylurea, but many other ureas derived from othersecondary amines may be obviously used. Compounds in which R; forms aring with R and/ or in which R and R form a ring are also contemplated,such as the urea formed from piperidine. Compounds in which R or R formsa ring with either R or R may also be used. N,N'-dialkyl substitutedethylene-ureas are representative of ureas having this configuration.

'5 The alkylated sulfonamides can be represented by the general formula:

RgSOgN wherein R R and R may be independently selected as long as thetotal number of carbon atoms contained in the three groups does notexceed and wherein R R and R may be alkyl, cycloalkyl or arylalkyl. Rmay be also aromatic, R or R may be hydrogen, whereby the N-alkylsulfonamide is obtained. A mixture of N-ethyl ortho and para toluenesulfonamides is a useful solvent of this class. Such a mixture is thecommercially available Santicizer 8 (obtainable from the Monsanto Chemical Co.) which contains about equal parts of the ortho and para isomersand minor amounts of unsubstituted sulfonamides. Normally, the R R and Rsubstituents should be selected so that the sulfonamide is a liquid or alow melting solid. Cyclic structures involving R and R are contemplatedfor the sulfonamides in the same manner disclosed for the carboxylicacid amides and the ureas. Representative sulfonamides includeN,N-diethyl ethanesulfonamide, N-butyl neopentylsulfonamide,N,N-dimethyl benzenesulfonamide, N-ethyl-N-methyl benzenesulfonamide,N-N-diethyl toluene-a-sulfonamide, N-ethyl toluene-a-sulfonamide, andN-methyl-N-ethyl p-toluenesulfonamide.

The above-described cyclic amides, viz alkylated cyclic amides, cyclicureas, and cyclic sulfonamides are included within the naming of theirrespective species of solvents.

Alkylated sulfoxides and the sulfones represent two other solvent typeswhich are useful in the present invention. The sulfoxides may berepresented by the formula:

u- IS -R12 and the sulfones by wherein R R R and R may be alkyl,cycloalkyl or aralkyl, selected so that the total number of carbon atomscontained in R plus R or in R plus R is no greater than 8. Cyclicstructures formed by R and R or by R and R are also contemplated.Representative of these two solvent types are dimethyl sulfoxide,dimethyl sulfone, diethyl sulfoxide, diethyl sulfone, dibutyl sulfone,tetramethyl sulfoxide, and tetramethyl sulfone.

When super solvents are employed other solvents can also be present toact as diluents or thinners. Preferably, the diluents are more volatilethan the super solvents such as fluorinated hydrocarbons or lowmolecular weight fluorochlorocarbons. The diluents can be gasses atatmospheric temperature and pressure and the mixture of super solventsand polycarbodiimide applied to the surface of the cellulosic web with aspray nozzle attached to a pressure vessel containing thepolycarbodiimide, the super solvent and the diluent, e.g. from anaerosol bomb.

The polycarbodiimides can also be applied to the cellulosic web in theform of emulsicins or dispersions. The emulsions can be prepared bymixing a polycarbodiimide solution in an organic solvent with an aqueousphase containing minor amounts of surface active agents dispersingagents or other conventional aids in the manufacture of emulsions.Liquid polycarbodiimides can be used in place of polycarbodiimidesolutions. The surface active agents include non-ionic, anionic andcationic types such as are described in the Encyclopedia or SurfaceActive Agents Sicily and Wood, Chemical Publishing Company, Inc., NewYork, N.Y., vol. 1, 1952 and vol. 2, 1964. In general, agents which donot cause excessive foaming, which are relatively insensitive to pHchanges, and which do not react readily with carbodiimide groups arepreferred. In addition to conventional surfactants of the type describedhereinabove, other materials such as methyl cellulose may be used tothicken the emulsions, thus aiding emulsion formation and retardingphasing. Methyl cellulose may also be considered an emulsifying agent inits own right for preparing the emulsions. Finely divided insolublesolids such as bentonite clay or estersils can also be used to stabilizethe emulsions.

The emulsions or dispersions can be prepared conventionally by batch orcontinuous processes. The organic phase can be liquid polycarbodiimide;a liquid mixture of a polycarbodiimide and a non-volatile plasticizer; asolution of polycarbodiimide in a volatile solvent (which can bestripped off before paper treatment if desired). In general the organicphase containing the polycarbodiimide is vigorously mixed with anaqueous phase which usually contains stabilizing agents; however, thestabilizers may be added as a part of the organic phase. Methylcellulose is an example of this type. The stabilizing agents may also beadded after the organic and aqueous phases have been given a preliminarymixing. The order in which the phases are mixed is not critical, but itis frequently more convenient to add the organic phase to the lessviscous aqueous phase. In preparing the emulsions or dispersions it ispreferred to make a concentrated composition by mixing approximatelyequal proportions of the organic and aqueous phases. The concentratedemulsions or dispersions produced can be diluted to any desiredconcentration by the addition of water. The compositions can, however,be prepared directly at low concentrations if so desired. The solutions,emulsions, or dispersions may contain minor amounts of additives of thetype normally employed in coating the adhesive formulations, preferablyof a type that do not react with the polycarbodiimide. Antioxidants,pigments, fillers, resins, plasticizers, for example, may be mixed ordispersed in the solutions, emulsions, or dispersions at any time priorto the paper treatment. These additional materials may be retained inthe coated paper.

The coating operation, Whether using solutions, dispersions oremulsions, can be performed in a variety of conventional ways such assizing, spraying, brushing, padding, wiping, roll coating, and dipping.The methods exemp lified hereinafter are merely illustrative; norestriction is intended. In a representative embodiment of sizing, apolycarbodiimide emulsion (or dispersion) is placed in the upper nip ofa pair of horizontally co-acting rollers and paper is passed downwardlytherebetween. In contrast to saturation i.e. immersion of the cellulosicweb in a solution of the aromatic polycarbodiimide, sizing appears toproduce an external coating and does not enter the interior portion ofthe cellulosic substrate. A Butter worth coater is an example of acommercially available device for performing the sizing operation. Inone method of surface coating with solutions the cellulosic web isimmersed for 10 seconds at room temperature in 210% by weight solutionof an polycarbodiimide in dimethylformamide.

After the coating composition containing the polycarbodiimide and theliquid carrier has been deposited on the paper, heat is applied toremove the carrier. The amount of heat needed will depend on factor suchas the proportion of carrier and its volatility under the prevailingpressure. The amount of heat supplied to a particular area will bedetermined by the temperature of the heating zone and the residence timeof the coated paper in it. If intense heat is provided, quick passage ofthe coated area through the zone will suffice; conversely, more moderateheating will require a longer residence time. The proper combination canreadily be determined by those skilled in the art to suit the equipmentavailable and the coating composition at hand. When aqueous dispersionor emulsions are involved it is frequently convenient to heat 7 at 100C. to 200. C. for about 1 to 30 minutes; 175 C. for 5 minutes ispreferred.

The heating step provides an unexpected additional benefit. It has beenfound that the properties of the polycarbodiimide coated paper can beimproved still more if heat is applied for a short while after thenormal drying is finished. As is shown more particularly hereafter in anexample, a sharp improvement can be obtained within 5 minutes. Theimprovement is more pronounced as the temperature is raised, but goodresults are noticed at temperatures as low as 100 C. and at least ashigh as 175 C.-200 C. In this heating step, there is generally a rapidgain in properties early in the cycle; continued heating may givefurther benefit but at a reduced rate. Those skilled in the art canselect the appropriate time for heating based on the improvement neededand practical considerations of cost and the like.

The upper temperature limit will be governed, in any case, by thestability of the paper itself. Excessive heating will embrittle or charit.

After the paper has been coated with the polycarbodiimide, the resultantarticle will display the improvements mentioned before. It is possible,although not clearly established, that under some circumstances thepolycarbodiimide undergoes one or more reactions which involve at leastpart of its N=C=N- groups. For example, they may form a few crosslinksof the type They may react with atmospheric water or residual water inthe paper to form urea groups, although the Campbell et al. publication[J. Org. Chem. 28, 2070 (1963)] indicates that polycarbodiimides arerather stable even under drastic conditions. Alternatively, they mayreact with carboxyl groups in the paper to form acyl urea groups; lesslikely, they may be attacked by hydroxyl groups Speculatively, theextent of these reactions may depend on factors such as the temperature,the nature of the carbodiimide polymer, and the type of liquid carrierused to deposit the polymer.

The coated cellulosic webs of the present invention all showimprovements in physical properties such as tensile strength andcompressive strength, better abrasion and better scuff resistance, underdry, humid, and under moist conditions. When solution coating techniquesare employed using super solvents in the absence of water, the wetstrength properties of the cellulosic webs as so treated are verysubstantially improved over the properties of cellulosic webs treatedwith the polycarbodiimides in ordinary solvents. The reason for thisdistinction is not known but it is speculated that a super solventproduces a more favorable disposition of the polycarbodiimide in theweb. When water forms at least a part of the carrier, as when the supersolvents are used in formulating an emulsion, the super solvents displayno particular advantage over the other solvents.

This invention is further illustrated by the following examples whichare not however intended to fully delineate the scope of this invention.In these examples the following test methods and definitions areempolyed.

The rigidity was measured by the short column crush test. In this test apaper specimen 1 x 4 inches is placed lengthwise in a clamp allowing alinear 0.25 x 4 inch strip to extend outside the holder. The strip ofpaper is then compressed between the platens of a Hinde-Dauch Percentpickup X 100 crush tester and the maximum load applied at failure ismeasured. All compressive strength tests were conducted in the crossdirection and are reported in pounds. All data represent average of 4tests. The wet compressive strength was measured immediately aftercomplete water immersion of the test specimens for 10 mins. or 24 hoursas specified. The compressive strength at relative humidity wasdetermined immediately after aging had been carried out at 90% relativehumidity/ F. for 72 hours. The dry compressive strength was measuredafter the paper had been stored at 50% relative humidity/ 75 F. for 24hours.

Tensile strength The tensile strength was determined on one-inch widepaper specimens in the machine direction with an Instron tester operatedat a crosshead speed of 2 in./min. with a 2-inch span employed betweenthe jaws. The results are reported in lbs/in. of width and are averagesof 2 tests. The wet tensile strength of the paper was measuredimmediately after water immersion for ten minutes at 75 F.

Burst strength The burst strength of the paper was determined with aMullen burst tester according to Tappi T403 immediately after the paperhad been immersed in water for 24 hours at 75 F. The results areaverages of 4 individual tests.

Abrasion resistance A continuous belt abrader (Custom ScientificInstrument) was used for these tests, the number or cycles (averages of2 runs) being determined when the paperboard failed completely and wastorn by the abrasive (grit size 320). The abrasion tests were conductedin the cross direction employing a load of 2.5 lbs.

EXAMPLE I A. Preparation of aromatic polycarbodiimide 112 parts of amixture containing toluene 2,4-diisocyanate and 20% of toluene2,6-diisocyanate were introduced under dry nitrogen into a clean dryreaction kettle which contained an atmosphere of dry nitrogen and wasequipped with an agitator. After the charge had been cooled under drynitrogen to a temperature below 20 C., 0.43 part of 1-phenyl-3-methyl3-phospholine-1-oxide catalyst was introduced. Immediately thereafterthe nitrogen stream was turned off and measurement of the carbon dioxideevolution was begun. The reaction mixture was slowly warmed to 45 C.over a period of about 5 hours. After 22.3 parts of carbon dioxide hadbeen evolved, 11.90 parts of isopropyl alcohol were immediately added tostop the polycarbodiimide formation. The mixture was then heated to atemperature of 85:2" C. over a period of 2 hours. The melt obtained wasdischarged and allowed to crystallize at room temperature.

The polycarbodiimide had an average-molecular weight of about 800(corresponding to an average of 4 N:C:N

groups) and melted in the range of 8085 C.

B. Coating of kraft linerboard of the aromatic polycarbodiimide Kraftlinerboard (weighing 42 lbs/1000 sq. ft.) was immersed for 10 seconds at25 C. in dimethylformamide solution containing 9.2, 4.6, and 2.3 weightpercent respectively of the polycarbodiimide of part A. The treatedboard was then dried at C. for 30 minutes and kept at 50 relativehumidity at 75 F. for 20 hours prior to testing.

For comparison an experiment outside the scope of the present inventionwas conducted. Procedure of part B above was essentially repeatedsubstituting N,N-di-otolylcarbodiimide for the polycarbodiimide of partA.

The data summarized in Table I show that polycarbodiimides are highlyefiective in improving the compressive strength of linerboard, whilemonocarbodiimides have practically no eifect at all.

The effect of heat treatment upon the compressive moved by fractionaldistillation at reduced pressure. The undistilled polyisocyanatecontains about 85% of volatile toluene diisocyanates, the remainderbeing phosgenation by-products.

strength of linerboard treated with the polycarbodiimide 5 Preparatlonof polylsocyanate mlxture B of part A according to the procedure of partB described Crude 4,4-diaminodiphenylmethane, containing about above isshown in Table IA. It is evident from the data polyarnines, is preparedby adding 1 mole of aquethat heating of the coated paper at temperaturesof 100 ous formaldehyde to an aqueous solution of 3 moles of C. to 175C. results in greatly improved compressive aniline and 2.8 moles ofhydrochloric acid at about strength under high humidity conditions. 1030 C., followed by heating at 85 C. for 3 hours. The TABLE IPolyoarbodiimide Monoearbodiimide l Untreated 2.5? 5.57 9.07 4.27 6.1lroperty Unit Control Pickup Pickup Pickup Picku Pickup AbrasionResistance 145 225 280 395 Wet compressive Strength 4.05 7.9 13.0 20.74.5 5.8 Compressive Strength at 90% relative humidity 16 .2 20.9 26 .535 .7 17.8 18 .7 Dry Compressive Strength 25 .2 28.1 34.1 49 .1 25.2 26.2

1 Outside the scope of the present invention; included for purpose ofcomparison. 2 After 24 hours water immersion at 75 F.

TABLE IA Heat Treatment 100 C. 150 C. 175 C. Untreated Air PropertyControl Dried 5 min. min. 5 min. 20 min. 5 min. 20 min. Pickup, Percents .85 9 .3 9 .35 8.8 8.6 8.65 7.85 Compressive Strength at 90% relativehumldlty (lbs 16 .6 24 .0 32 .0 30 .5 34 .8 35 .1 36 .2 39 .4 WetCompressive Strength 1 (lbs) 4.0 7.2 10.5 11.5 17.1 18.6 20.0 23.5

1 10 min. water immersion.

EXAMPLE II A. Emulsification of polycarbodiimides Over a period of oneminute a solution of parts of the polycarbodiimide of Example I in 35parts of methylene chloride was added slowly with continuous agitationto an aqueous solution containing 10 parts of 10% Aquarex D wettingagent, parts of 10% aqueous ammonium caseinate, and 60 parts of water at25 C. Aquarex D wetting agent (available from E. I. du Pont de Nemours &Co.) is a mixture of sodium salt of sulfate monoesters of a mixture ofhigher fatty alcohols consisting chiefly of the lauryl and myristylderivatives of the type RSO Na. High speed agitation was continued forone more minute. The resulting emulsion was very white in color stablefor at least one hour at 25 C. (no settling of solids or foaming tookplace) and resembled shaving lather.

B. Paper treatment with polycarbodiimide emulsions The aqueous emulsionof the polycarbodiimide made in part A above was applied to 42-lb.linearboard by sizing techniques using a Butterworth coater. The paperwas then dried immediately by passing it through a paper drum dryer. Forpurposes of comparison, linerboard, which had not been coated, wastested at the same time as the sample made above. Table II gives thedata obtained for all these samples.

condensation mass is then neutralized with sodium hydroxide. The organiclayer subsequently separated from it is freed from unreacted aniline bydistillation at reduced pressure. The mixture of diand higher polyaminesleft behind in the still pot is dissolved in o-dichlorobenzene andconverted to the corresponding isocyanates by phosgenation followingesentially the procedure disclosed in U.S. Patent 2,822,373. After thephosgenation, the odichlorobenzene is removed by fractional distillationat reduced pressure. The undistilled product left behind contains about72% 4,4'-diisocyanatodiphenylmethane. The rest of the mixture consistsof polyisocyanates and phosgenation by-products. The product containsabout 31% by weight of isocyanato groups when assayed by the procedureof ASTM D163 8-60T.

A. Preparation of polycarbodiimides Polycarbodiimide 1.A mixtureconsisting of 10 parts of polyisocyanate mixture A, 50 parts ofdimethylformamide and 0.2 part of phospholine oxide catalyst describedin Example I (part A) was heated at 50? C. for 2 hours While stirredunder dry nitrogen. The resulting polycarbodiimide formation caused theNCO-group content of the reaction mixture to drop from 7.0% to 1.1%. TheNCO-terminated polycarbodiimide obtained was capped by adding anequivalent amount of aniline (1.5 parts). The resulting solution of theurea-terminated polycarbodi- TABLE II.--SIZING OF 42-LB. LINERBOARD WITHPOLYCARBODIIMIDE- WATER EMULSIONS Dry Compressive Compressiv Strength at90% p, Drying Strength Relative Wet Burst Percent Dry Weight Conditions(Lbs) Humidity (Lbs) (Points) s min/285 No drying min./302 F EXAMPLE IIIPreparation of polyisocyanate mixture A Tolylene diamine (80%2,4-isomer; 20 2,6-isomer) is dissolved in o-dichlorobenzene andphosgenated essentially by the procedure disclosed in U.S. Patent2,822,373. Following the phosgenation, o-dichlorobenzene is repholineoxide catalyst of Example 1. After a reaction time of about 45 minutesthe NCO-group content of the reaction mixture was reduced from 4.24% to1.74%. The resulting NCO-terminated polycarbodiimide was capped with 4parts of aniline by the procedure described for polycarbodiimide 1.

Polycarbodiimide 3.-An NCO-terminated polycarbodiimide was prepared byheating 10 parts of polyisocyanate mixture B at 60 C. for 70 minutes inthe presence of 100 parts of dimethylformamide and 0.1 part of thephospholine oxide catalyst of Example 1. Polycarbodiimide 3 was made bycapping the isocyanate end groups with isopropyl alcohol (2.0 parts) at60 C.

B. Application of dimetliylformamide solutions of polycarbodiimides Thepolycarbodiimides described in part A were applied on kraft linerboardby essentially the same procedure as described in Example 1, part B. Thetesting results shown in Table III demonstrate the greatly improved dryand wet properties of polycarbodiimide treated linerboard in comparisonwith the untreated linerboard.

A similar improvement to that described in paragraph 1 above wasobserved when corrugating medium (basis weight 33 lb./ 1000 sq. it.) wastreated with the polycarbodiimide solutions of part A by the samesaturation technique.

12. EXAMPLE v A. Preparation of Polycarbodiimide solution One hundredparts of polyisocyanate mixture A, described in Example III wereagitated at C. in the presence of 0.2 part of the phospholine oxidecatalyst of Example I. The temperature Was slowly raised to 60 within 3hours and maintained at this value until the NCO-group content of thereaction mixture was reduced to about 20%. Then isopropyl alcohol parts)was added for end group capping While the temperature was kept at 60 C.for another hour. Dilution of the resulting urethane-terminatedpolycarbodiimide with 30 parts of a representative super solvent amixture of N-ethyl-oand N-ethyl-p-t0luene sulfonamide 1 (30 parts)yielded a solution which was a very viscous liquid at 25 C.

Coniimereially available from Monsanto Chemical Co. as Santicizer 8 B.Application of dimethylformamide solution of the polycarbodiimide TABLEIII Polycarbodilrnide No. 1 Polyearbodiimide N0. 2 Polycarbodiimide No.3 Untreated 3. 0% 5. 5% 9. 0% 2.2 5.2% 10.6% 2. 1% 5. 2% 9.9% UnitControl Pickup Pickup Pickup Pickup Pickup P iekup Pickup Pieku p PickupWet Compressive Strength Pounds. 4.05 8. 5 13. 4 14. 4 5. 9 9. 3 16. 57. 3 12. 1 16. 7 Compressive Strength alter do 16. 2 21. 5 27. 5 29. 221. 2 26. 8 38.1 23. 6 30. 8 40. 5

aging at 90% relative humldlt 25. 2 25. 7 33. a 43. 1 9. 4 60. 5 90 102Elongation at Break Percent. 1. 2 3.05 3. 4 3. 5

1 10 minutes water immersion. B For comparison, the untreated linerboardexhibited a dry tensile strength of 105 1bS./ll1.

EXAMPLE IV TABLE v A. Preparation of polycarbodiimides P t C t 1 P k m kP 1 ro er on ro 10 u 16' 174 parts of the toluene diisocyanate isomermixture y P 0 up p t of Exam- Wet Compressive Strength L. 2. 1 6.0 9. 314. 8 and 0.35 part of the phospholine oxide cataly Compressive Strengthat 90% ple 1 were heated at 60 C. while agitated in a y fi relativehumidity 16.5 22. 9 27. 2 35.1 Dry Compressive Strength- 26. 0 31.8 32.6 41. 2

By minutes, 30.5 parts of carbon dioxide had been evolved. The reactionproduct was then capped by adding 100 parts of n-octanol to stop furthercarbodiimide formation. The resulting urethane-terminatedpolycarbodiimide A-l had a number-average molecular weight of about 700(corresponding to 2 N=C=N-- groups) and a melting range of -60 C.

The above-described polycarbodiimide preparation was essentiallyrepeated except that 2(2-ethoxyethoxy) ethanol was substituted forn-octanol. The liquid polycarbodiimide A-2 obtained had a number-averagemolecular weight of about 700.

B. Application of dimethylformamide solutions of polycarbodiimidesdescribed in part A The polycarbodiimides described in part A wereapplied on kraft linerboard by saturation as outlined in Example I, partB. The paper properties before and after treatment are shown in TableIV.

1 10 minutes water immersion.

EXAMPLE VI The procedure of Example I was repeated except that the supersolvent described therein was replaced by representative conventionalsolvents. The data obtained for the resulting coated cellulosicsubstrates are given in Table VI.

For comparison, the data obtained with a super solvent dimethylsulfoxide, are included. It is evident from these results that when asuper solvent is used during the paper treatment, the wet strengthproperties of the coated linerboard are substantially improved, ascompared with the properties displayed by linerboard treated with theair aid of ordinary solvents. N0 solvent effect was found in respect tocompressive strength under dry conditions or at relative humidity.

TABLE IV.-TREATMENT OF KRAFT LINERBOARD WITH AROMATIC POLYCARBODIIMIDESPolycarbodiimide A-l Polycarbodiimide A-2 Untreated 2. 1% 4. 57 8. 67 2.6 7 4. 97 8. 07 Property Unit Control Pickup Pickup Pickug Picki ritkufiPicke Wet Compressive Strength 1 Pounds.--" 2.1 6.0 9.2 15.1 5.0 9.414.0 Compressive Strength at 90% relative humidity ..d0 16. 5 21. 3 24.5 29. 1 20. 2 24. 5 30. 6 Dry Compressive Strength .d0 26. 0 26. 0 30. 536. 0 24.0 28.1 36.1

l 10 minutes Water immersion.

TABLE VI Untreated Methylene Dimethyl- Eth l Tet Solvent ControlChloride Toluene sulfoxide 1 Aceta te hydroil l ran Pickup, percent dryweight l0. 9 5. 7 2. 3 5. 9 2. 9 1. 0 7. 7 3 7 6. 1 2. 7 0. 7 7. 8 3.9 1. 3 Wet Compressive strength (lbs.) 2 2. 2 8.9 7. 2 6. 6 5. 6 5. 3 4.7 14. 30 6 7 6. 4 5. 9 4. 8. 3 6.9 5. 6 Compressive Strength at 90%relative humidity (lbs.) 20. 6 36 29 27. 3 31 27 23 29 23 33 28 24 34 2722 Dry Compressive Strength (lhs.) 26 51 43 35 43 38 32 44. 3 26. 0 4235 31 48 36 30 Dry Tensile Strength (lbs/1n.) 102 149 136 132 145 133129 Wet Tensile Strength (lbs/in.) 16 66 53 35 84 65 Super solvent. 2mlnutes water immersion.

EXAMPLE VII 30 parts of the polycarbodiimide described in Exampledimethylformamide. Typical data obtained from the resulting coatedlinerboard are shown in Table VIII.

TABLE VIII Untreated Untreated Property Control 1 Polycarbodiimide 1Control 2 Polycarbodiimide 2 Pickup, percent 4. 7 7. 9 4.0 8.1Compresslve Strength at 90% relative humidity (lbs.) 24.1 29. 9 37. 117. 2 22. 25. 9 Dry Compressive Strength (lbs.) 33.1 37. 6 44. 3 23.033. 8 37. 8

1 For Polycarbodiimide 1.

I was dissolved in methylene chloride (70 parts). The resulting lowviscosity solution was sprayed on linerboard (42-lb. basis weight) withan air brush sprayer. After the spraying operation the paper was driedin a drum drier for 8 minutes at 285 F. The data obtained from thetreated liner are shown in Table VII.

EXAMPLE VIII A. Preparation of polycarbodiimides Polycarbodiimide 1.Amixture consisting of (a) 94.2 parts of o-tolylisocyanate, (b) 123.5parts of a mixture containing 80% of toluene 2,4-diisocyanate and oftoluene 2,6-diisocyanate, and (c) 0.75 part of phospholine oxidecatalyst described in Example 1 (part A) is heated at 60-65" C. forseveral hours until the -NCO group content of the reaction mixture isreduced to 0.65%. The resulting polycarbodiimide composition is aviscous liquid at C. and contains about 23% of monocarbodiimide.

Polycarbodiimide 2.-3.6 parts of tetraisopropyl titanate are added to astirred refluxing mixture consisting of 23.6 parts ofmethylene-bis(4-cyclohexylisocyanate) obtained by phosgenation ofmethylene-bis(4-cyclohexylamine) and having the following isomercontent: 50% trans-trans, 40% cis-trans, 8% cis-cis and 2% 2,4-isomet)and 90 parts of monochlorobenzene. After 2.64 parts of carbon dioxideare evolved (4-5 hours reaction time) 7.5 parts of cyclohexylisocyanateare added. The reaction is completed by heating at reflux temperaturefor an additional 16 hours until another 2.64 parts of carbon dioxideare evolved. The resulting polycarbodiimide solution is free ofisocyanato groups.

B. Application of solutions of polycarbodiimide The polycarbodiimidesdescribed in part A are applied on kraft linerboard by essentially thesame procedure as described in Example I except that forpolycarbodiimide 2 monochlorobenzene is used as solvent instead of N,N-

2 For Polycarbodiimide 2.

What I claim is:

1. An article of manufacture comprising a cellulosic web having at leastone surface coated with an organic 25 polycarbodiimide, the coatingbeing 1 to 15% by weight of the cellulosic web and the polycarbodiimidecontaining from 2 to weight percent of carbodiimide groups.

2. Article of claim 1 in which the organic polycarbodiimide is anaromatic polycarbodiimide.

3. Article of claim 1 in which the organic polycarbodiimide is a polymerof a mixture comprising toluene diisocyanates.

4. Article of claim 1 in which the organic polycarbodiimide is a polymerof 4,4-diisocyanato diphenylmethane.

5. Article of claim 1 in which the organic polycarbodiimide is a polymerof S-chloro-toluene diisocyanate.

6. Article of claim 1 in which the said organic polycarbodiiimide is apolymer of methylene bis(4-cyclohexylisocyanate).

7. Article of claim 2 in which the aromatic polycarbodiimide is urethaneterminated by reaction with an aliphatic alcohol having from 8 to 20carbon atoms.

8. Article of claim 2 in which the aromatic polycarbodiimide isterminated by reaction with an organic monoisocyanate.

References Cited UNITED STATES PATENTS 2,941,966 6/1960 Campbell.

2,941,983 6/1960 Smeltz 117-139.5 X 2,955,095 10/1960 Gollob 117-155 X2,987,494 6/1961 Black 117-161 X 3,152,131 10/1964 Heberling 260-2883,157,662 11/1964 Smeltz 260-288 3,178,310 4/1965 Berger et al 117-155 X3,226,368 12/1965 Reischl et al 117-161 X 3,282,897 11/1966 Angelo117-161 X 3,282,898 11/1966 Angelo 117-161 X 3,345,342 10/1967 Angelo117-161 X WILLIAM D. MARTIN, Primary Examiner.

M. LUSIGNAN, Assistant Examiner.

US. Cl. X.R.

